oopMapCache.hpp revision 1472:c18cbe5936b8 
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24
25// A Cache for storing (method, bci) -> oopMap.
26// The memory management system uses the cache when locating object
27// references in an interpreted frame.
28//
29// OopMapCache's are allocated lazily per instanceKlass.
30
31// The oopMap (InterpreterOopMap) is stored as a bit mask. If the
32// bit_mask can fit into two words it is stored in
33// the _bit_mask array, otherwise it is allocated on the heap.
34// For OopMapCacheEntry the bit_mask is allocated in the C heap
35// because these entries persist between garbage collections.
36// For InterpreterOopMap the bit_mask is allocated in
37// a resource area for better performance.  InterpreterOopMap
38// should only be created and deleted during same garbage collection.
39//
40// If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used
41// per entry instead of one. In all cases,
42// the first bit is set to indicate oops as opposed to other
43// values. If the second bit is available,
44// it is set for dead values. We get the following encoding:
45//
46// 00 live value
47// 01 live oop
48// 10 dead value
49// 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)
50
51
52class OffsetClosure  {
53 public:
54  virtual void offset_do(int offset) = 0;
55};
56
57
58class InterpreterOopMap: ResourceObj {
59  friend class OopMapCache;
60
61 public:
62  enum {
63    N                = 2,                // the number of words reserved
64                                         // for inlined mask storage
65    small_mask_limit = N * BitsPerWord,  // the maximum number of bits
66                                         // available for small masks,
67                                         // small_mask_limit can be set to 0
68                                         // for testing bit_mask allocation
69
70#ifdef ENABLE_ZAP_DEAD_LOCALS
71    bits_per_entry   = 2,
72    dead_bit_number  = 1,
73#else
74    bits_per_entry   = 1,
75#endif
76    oop_bit_number   = 0
77  };
78
79 private:
80  methodOop      _method;         // the method for which the mask is valid
81  unsigned short _bci;            // the bci    for which the mask is valid
82  int            _mask_size;      // the mask size in bits
83  int            _expression_stack_size; // the size of the expression stack in slots
84
85 protected:
86  intptr_t       _bit_mask[N];    // the bit mask if
87                                  // mask_size <= small_mask_limit,
88                                  // ptr to bit mask otherwise
89                                  // "protected" so that sub classes can
90                                  // access it without using trickery in
91                                  // methd bit_mask().
92#ifdef ASSERT
93  bool _resource_allocate_bit_mask;
94#endif
95
96  // access methods
97  methodOop      method() const                  { return _method; }
98  void           set_method(methodOop v)         { _method = v; }
99  int            bci() const                     { return _bci; }
100  void           set_bci(int v)                  { _bci = v; }
101  int            mask_size() const               { return _mask_size; }
102  void           set_mask_size(int v)            { _mask_size = v; }
103  int            number_of_entries() const       { return mask_size() / bits_per_entry; }
104  // Test bit mask size and return either the in-line bit mask or allocated
105  // bit mask.
106  uintptr_t*  bit_mask()                         { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
107
108  // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
109  size_t mask_word_size() {
110    return (mask_size() + BitsPerWord - 1) / BitsPerWord;
111  }
112
113  uintptr_t entry_at(int offset)            { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
114
115  void set_expression_stack_size(int sz)    { _expression_stack_size = sz; }
116
117#ifdef ENABLE_ZAP_DEAD_LOCALS
118  bool is_dead(int offset)                       { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
119#endif
120
121  // Lookup
122  bool match(methodHandle method, int bci)       { return _method == method() && _bci == bci; }
123  bool is_empty();
124
125  // Initialization
126  void initialize();
127
128 public:
129  InterpreterOopMap();
130  ~InterpreterOopMap();
131
132  // Copy the OopMapCacheEntry in parameter "from" into this
133  // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
134  // allocated space (i.e., the bit mask was to large to hold
135  // in-line), allocate the space from a Resource area.
136  void resource_copy(OopMapCacheEntry* from);
137
138  void iterate_oop(OffsetClosure* oop_closure);
139  void oop_iterate(OopClosure * blk);
140  void oop_iterate(OopClosure * blk, MemRegion mr);
141  void verify();
142  void print();
143
144  bool is_oop  (int offset)                      { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
145
146  int expression_stack_size()                    { return _expression_stack_size; }
147
148#ifdef ENABLE_ZAP_DEAD_LOCALS
149  void iterate_all(OffsetClosure* oop_closure, OffsetClosure* value_closure, OffsetClosure* dead_closure);
150#endif
151};
152
153class OopMapCache : public CHeapObj {
154 private:
155  enum { _size        = 32,     // Use fixed size for now
156         _probe_depth = 3       // probe depth in case of collisions
157  };
158
159  OopMapCacheEntry* _array;
160
161  unsigned int hash_value_for(methodHandle method, int bci);
162  OopMapCacheEntry* entry_at(int i) const;
163
164  Mutex _mut;
165
166  void flush();
167
168 public:
169  OopMapCache();
170  ~OopMapCache();                                // free up memory
171
172  // flush cache entry is occupied by an obsolete method
173  void flush_obsolete_entries();
174
175  // Returns the oopMap for (method, bci) in parameter "entry".
176  // Returns false if an oop map was not found.
177  void lookup(methodHandle method, int bci, InterpreterOopMap* entry);
178
179  // Compute an oop map without updating the cache or grabbing any locks (for debugging)
180  static void compute_one_oop_map(methodHandle method, int bci, InterpreterOopMap* entry);
181
182  // Helpers
183  // Iterate over the entries in the cached OopMapCacheEntry's
184  void oop_iterate(OopClosure *blk);
185  void oop_iterate(OopClosure *blk, MemRegion mr);
186  void verify();
187
188  // Returns total no. of bytes allocated as part of OopMapCache's
189  static long memory_usage()                     PRODUCT_RETURN0;
190};
191